1. Field of the Invention
The present invention relates to an ink on the basis of solvents for ink jet printing systems, particularly continuous jet systems. The invention also relates to a method of using the ink for printing on rubber or silicone.
2. Description of the Related Art
Inks used in ink jet printing technology for printing on various rubber materials are known in principle. Such inks are essentially composed of solvents, coloring agents and binding agents. Pigments as well as dyes are used as coloring agents.
A disadvantage of such inks is their insufficient abrasion resistance and insufficient bonding to various types of plastics materials, especially on various types of rubber and silicone.
For evaluating the adherence, frequently the so called adhesive film test is used. When this test is performed, a film is placed on an area imprinted with ink, the film is pressed on and then pulled off again. In this test, a measure of the adherence of the ink on the substrate is the quantity of the ink residues which adhere to the adhesive film and which have been separated from the printed area when the film was pulled off.
It has also been found to be disadvantageous that markings printed on such plastics materials, especially rubber and silicone, can easily be rubbed off with the fingers or wear off quickly during daily use, and the imprints, which sometimes contain important information, become illegible or unattractive.
For example, EP 0 730 014 A1 discloses an ink jet ink for printing on non-porous surfaces, such as glass, metal or plastic containers, wherein the imprints are supposed to have a high rub resistance to alcohol. These inks have the disadvantage that their adherence to rubber and silicone is insufficient. A large portion of the imprint is separated from the printed surface when the adhesive film test is performed.
U.S. Pat. No. 4,168,254 discloses an ink jet ink for printing on cables encased in polymer, wherein the ink contains a resin for fixing the coloring agent on a substrate. Such an ink has the disadvantage that the abrasion resistance is achieved only by heating to a high temperature. The supplied heat activates a chemical reaction which causes cross-linking of the binding agent.